1. Field of the Invention
The present invention is directed to an autoradiography system for exposing, storing and reading out a latent image of a tissue preparation made self-stimulable.
2. Description of the Prior Art
Autoradiography systems are known which include a cassette which receives a preparation of tissue to be examined made self-radiating by a suitable radioisotope, and a phosphor foil which records radiation from the tissue sample. After exposure to the preparation, the latent image in the phosphor foil is read out by a suitable scanning beam, and the resulting light is detected and electronic signals generated therefrom, from which a visual image is obtained.
The tissue preparation may be made, for example, from bone cells or carcinoma cells, and the preparation made therefrom is brought into direct contact with the phosphor foil.
A filmless autoradiography system is described in the periodical "Nature" Volume 326, Apr. 16, 1987 at page 725. In this system, the replacement of conventional x-ray film with a stimulable phosphor foil is disclosed. After exposure by the radiation-emitting preparation, the stimulable phosphor foil is scanned by a laser, so that the phosphor foil emits light corresponding to the latent image stored therein. The emitted light is acquired by a detector, the output signal of which is converted into a digital signal which is supplied to a computer for storage, analysis and processing. A visible image can be viewed on a monitor. Because such stimulable phosphor foils are more sensitive than conventional x-ray film at the radiation levels occurring in autoradiography, the stimulable phosphor foil is thus also exposed to scattered radiation produced by cosmic rays, in addition to being exposed to the useful radiation of the tissue preparation. Such exposure to cosmic rays occurs predominately during the time the foil is being exposed to the tissue preparation. The disturbances caused by the cosmic ray appear in the resulting image as pronounced point patterns, and thus limit the sensitivity of the system. Given longer exposure times, a further source of noise occurs, namely the thermal noise of the stimulable phosphor itself, so that the image quality may be further deteriorated.